1. Field of the Invention
The invention relates to a fan motor which is mainly used in civil heating and ventilation air-conditioning (HVAC) systems.
2. Description of the Related Art
The improvement of the efficiency of HVAC systems reduces energy consumption greatly. For example, the utilization efficiency of many high-efficient stoves, air conditioners, and air cleaners (AFUE rated value) now is above 90%. However, the efficiency of fan motors which are used to move the air in these systems doesn't improve obviously yet and is too low. As the total energy consumption of HVAC systems which belong to fan motors increases when the stoves and air conditioners are more efficient, the fan motors become larger contributors of the whole systems in terms of energy consumption.
The reason of the low efficiency is that the fan motors of HVAC systems are fixed-speed or multi-speed permanent-split capacitor (PSC) motors. These motors usually have at least two independent power connectors which are used to demodulate the heating or cooling mode of operation. The heating or cooling power input end is usually connected to different winding taps of the PSC motors, which can provide different operating speeds to some extent for different operational modes.
The PSC motor can be designed to have more than two taps, which allows OEMs (original equipment manufacturers) or installation mechanics to choose operating speeds by connecting the taps to heating or cooling power connecting wire respectively. The electric energy of these AC power connecting wires connected to the motor can be controlled by a temperature switch; the relays are driven by a thermostatic controller.
FIG. 1 shows other fixed speed PSC motors used for civil HVAC systems. The motor has four winding taps to demodulate the speeds of two heating fans and two cooling fans. The speeds of the fans are controlled by a stove control panel which has a cooling/heating relay, a high/low cooling relay and a high/low heating relay. Other HVAC systems consist of two heating stages and a single cooling stage, or some other combinations of heating and cooling revolving speeds.
When operating at a high speed, the PSC motor is reasonably efficient; when operating at a low speed, its efficiency can lower to within 20%. As the air flow needed by the evaporator coil of the air conditioner is faster than that of the heat exchanger of the stove, the efficiency of the fan motor running at a lower speed is low during the period of the operation of the stoves. During the period of continuous operation of the fan, the efficiency of the fan motor is lowest when it is still running at a lower speed.
Due to the low efficiency of the PSC motors, many updated HVAC systems apply variable speed motors such as brushless permanent-magnet motors (BPM) and corresponding variable speed motors with electronic controllers. The revolving speed of BPM can be controlled by electronic components, which is especially set to produce required air flow matching with each application. In addition, the power consumption of BMP is about in direct proportion to the cube of the motor speed, and the electrical work of the PSC motors is about in direct proportion to the motor speed. Hence, when the motor speed drops, the electrical work of BPM within the whole scope of motor speed is lower than that of BPM. As mentioned above, this is especially important when the fan runs continuously and repeatedly.
Variable speed motors are superior to PSC motors. To replace the existing PSC motors by variable motors, complicated changes in production cost, time consumption, machinery, wiring or system control configuration is necessitated. The variable motors which are used to replace the PSC motors in the existing HVAC systems have been developed already, but their control and sensing systems are relatively complex. In other alternative systems, to install alternative motors needs to supply continuous electrical power to the motors and directly send the lower-voltage control signals of the thermostatic controllers to the motors. It is very difficult to make these connecting wires in the existing HVAC systems. In addition, these systems known in the art are lack of sensitivity to the fan motors running at a low speed.
The restrictions of the existing PSC motors and BPM are that HVAC OEMs often need to configure motors with sole parameters (the torque load, the fan speed, the direction of rotation, etc.) and optimize the performance of HVAC components. Variable speed PSC motors and BPM provide some options; many operational parameters are set after manufacturing and are difficult to change. Therefore, motor manufacturers, installation mechanics and maintenance contractors have to have all kinds of stocks of fan motors to demodulate different modes of HVAC equipment.
Hence, it is hoped to provide an imbedded improved substitute for the PSC motors of the HVAC system which has advantages of the variable motors but doesn't change the original HVAC system obviously. More important is that it lowers the complexity of such alternative systems by using simple control circuits and cancels additional arrangements of wires which are usually used in connecting the regular variable speed motors and the existing alternative variable speed motors. Consequently, higher requirements are set on variable speed fan motors.